Integrated circuits using optical fiber interconnects formed through a semiconductor wafer

ABSTRACT

An integrated circuit with a number of optical fibers that are formed in high aspect ratio holes. The high aspect ratio holes extend through a semiconductor wafer. The optical fibers include a cladding layer and a core formed in the high aspect ratio hole. These optical fibers are used to transmit signals between functional circuits on the semiconductor wafer and functional circuits on the back of the wafer or beneath the wafer.

[0001] This application is a Divisional of U.S. application Ser. No.09/650,569, filed Aug. 30, 2000, which is a Continuation of U.S.application Ser. No. 09/031,975, filed on Feb. 26, 1998, now U.S. Pat.No. 6,150,188, both of which are incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

[0002] The present invention relates generally to the field ofintegrated circuits and, in particular, to integrated circuits usingoptical fiber interconnects formed through a semiconductor wafer andmethods for forming same.

BACKGROUND OF THE INVENTION

[0003] Electrical systems typically use a number of integrated circuitsthat are mounted on a printed circuit board. The individual integratedcircuits of the system are typically fabricated on different wafers.Each wafer is tested and separated into individual dies or chips.Individual chips are then packaged as individual integrated circuits.Each integrated circuit includes a number of leads that extend from thepackaging of the circuit. The leads of the various integrated circuits,are interconnected to allow information and control signals to be passedbetween the integrated circuits such that the system performs a desiredfunction. For example, a personal computer includes a wide variety ofintegrated circuits, e.g., a microprocessor and memory chips, that areinterconnected on one or more printed circuit boards in the computer.

[0004] While printed circuit boards are useful for bringing togetherseparately fabricated and assembled integrated circuits, the use ofprinted circuit boards creates some problems which are not so easilyovercome. For example, printed circuit boards consume a large amount ofphysical space compared to the circuitry of the integrated circuitswhich are mounted to them. It is desirable to reduce the amount ofphysical space required by such printed circuit boards. Further,assuring the electrical integrity of interconnections between integratedcircuits mounted on a printed circuit board is a challenge. Moreover, incertain applications, it is desirable to reduce the physical length ofelectrical interconnections between devices because of concerns withsignal loss or dissipation and interference with and by other integratedcircuitry devices.

[0005] A continuing challenge in the semiconductor industry is to findnew, innovative, and efficient ways of forming electrical connectionswith and between circuit devices which are fabricated on the same and ondifferent wafers or dies. Relatedly, continuing challenges are posed tofind and/or improve upon the packaging techniques utilized to packageintegrated circuitry devices. As device dimensions continue to shrink,these challenges become even more important.

[0006] For reasons stated above, and for other reasons stated belowwhich will become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art foran improved technique for interconnecting individual integrated circuitsin an electronic system.

SUMMARY OF THE INVENTION

[0007] The above mentioned problems with integrated circuits and otherproblems are addressed by the present invention and will be understoodby reading and studying the following specification. Integrated circuitsare described which use optical fibers that extend through the thicknessof a semiconductor substrate or wafer so as to allow communicationbetween integrated circuits formed on opposite sides of a single wafer,on opposite sides of two wafers that are bonded together, formed onwafers in a stack that are bonded together, or other appropriateconfiguration of wafers.

[0008] In one embodiment, a method for interconnecting first and secondintegrated circuits is provided. The first integrated circuit is formedon a working surface of a first semiconductor substrate. At least onehigh aspect ratio hole is formed through the first semiconductorsubstrate. An optical fiber with a cladding layer and a core is formedin the at least one high aspect ratio hole. The optical fiber havingfirst and second ends. The first integrated circuit is coupled to thesecond integrated circuit through the optical fiber. In one embodiment,the second integrated circuit is formed on a second surface of the firstsemiconductor substrate, opposite the working surface of the firstsemiconductor substrate. In another embodiment, the second integratedcircuit is formed on a working surface of a second semiconductorsubstrate. The second semiconductor substrate is bonded to the firstsemiconductor substrate such that the first and second integratedcircuits are coupled together through the optical fiber in the firstsemiconductor substrate. In another embodiment, the surfaces of thefirst and second semiconductor substrates that are bonded together arelocated on sides of the first and second semiconductor substrates thatare opposite the working surfaces of the first and second semiconductorsubstrates, respectively.

[0009] In another embodiment, an electronic system is provided. Theelectronic system includes at least one semiconductor wafer. A number ofintegrated circuits are also provided. At least one integrated circuitis formed on the at least one semiconductor wafer. The at least onesemiconductor wafer includes at least one optical fiber formed in a highaspect ratio hole that extends through the thickness of the at least onesemiconductor wafer. At least one optical transmitter and at least oneoptical receiver are associated with the at least one optical fiber. Theoptical transmitter and optical receiver transmit optical signalsbetween selected integrated circuits of the electronic system over theoptical fiber.

[0010] In another embodiment, an integrated circuit is provided. Theintegrated circuit includes a functional circuit formed on a wafer. Anumber of optical fibers are formed in high aspect ratio holes thatextend through the wafer. The optical fibers include a cladding layerand a center core that are formed from materials with different indicesof refraction.

[0011] In another embodiment, a method for forming an integrated circuitin a semiconductor wafer with an optical fiber that extends through thesemiconductor wafer is provided. The method includes forming afunctional circuit in a first surface of the semiconductor wafer. Anumber of etch pits are formed in the first surface of the semiconductorwafer at selected locations in the functional circuit An anodic etch ofthe semiconductor wafer is performed such that high aspect ratio holesare formed through the semiconductor wafer from the first surface to asecond, opposite surface. A cladding layer of an optical fiber is formedon an inner surface of the high aspect ratio holes. A core layer of theoptical fiber is also formed. The optical fiber is selectively coupledto the functional circuit.

[0012] In another embodiment, a method for forming an optical fiberthrough a semiconductor substrate is provided. The method includesforming at least one high aspect ratio hole through the semiconductorsubstrate that passes through the semiconductor substrate from a firstworking surface to a surface opposite the first working surface. Acladding layer of an optical fiber is formed on an inner surface of theat least one high aspect ratio hole. A core layer of the optical fiberis also formed. In one embodiment, the cladding layer comprises an oxidelayer formed in the high aspect ratio holes. In another embodiment, thecore layer comprises a layer of an oxide with an index of refractionthat is greater than the index of refraction of the cladding layer. Inanother embodiment, the core layer comprises a layer with a hole thatextends substantially along the length of the optical fiber with adiameter that is less than 0.59 times the wavelength of light used totransmit signals over the optical fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIGS. 1A, 1B, and 1C are elevational views of exemplaryembodiments of an integrated circuit with a semiconductor wafer havingan optical fiber formed in an high aspect ratio hole that extendsthrough the semiconductor wafer according to the teachings of thepresent invention.

[0014]FIGS. 2, 3, 4, 5, 6, and 7 are views of a semiconductor wafer atvarious points of an illustrative embodiment of a method for forming anintegrated circuit with optical fibers formed through at least onesemiconductor wafer according to the teachings of the present invention.

[0015]FIGS. 8 and 9 are graphs that show guided waves in optical fibersaccording to the teachings of the present invention.

DETAILED DESCRIPTION

[0016] In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific illustrative embodiments in which theinvention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized and that logical, mechanical and electrical changes may be madewithout departing from the spirit and scope of the present invention.The following detailed description is, therefore, not to be taken in alimiting sense.

[0017] In the following description, the terms wafer and substrate areinterchangeably used to refer generally to any structure on whichintegrated circuits are formed, and also to such structures duringvarious stages of integrated circuit fabrication. Both terms includedoped and undoped semiconductors, epitaxial layers of a semiconductor ona supporting semiconductor or insulating material, combinations of suchlayers, as well as other such structures that are known in the art.

[0018] The term “horizontal” as used in this application is defined as aplane parallel to the conventional plane or surface of a wafer orsubstrate, regardless of the orientation of the wafer or substrate. Theterm “vertical” refers to a direction perpendicular to the horizonal asdefined above. Prepositions, such as “on”, “side” (as in “sidewall”),“higher”, “lower”, “over” and “under” are defined with respect to theconventional plane or surface being on the top surface of the wafer orsubstrate, regardless of the orientation of the wafer or substrate.

[0019]FIG. 1A is an elevational view of an embodiment of the presentinvention. Electronic system 105 a includes semiconductor wafer 100 a.Semiconductor wafer 100 a includes at least one optical fiber 102 a thatprovides a path for transmitting signals between functional circuit 108a on a first surface of semiconductor wafer 100 a and functional circuit109 a on a second, opposite surface of semiconductor wafer 100 a. It isnoted that a number of optical fibers can be formed throughsemiconductor wafer 100 a.

[0020] Optical fiber 102 a is formed in a high aspect ratio hole insemiconductor wafer 10 a. The high aspect ratio hole is formed using,for example, an anodic etching technique as described in more detailbelow. Typically, the high aspect ratio holes have an aspect ratio inthe range of approximately 100 to 200. Conventionally, a semiconductorwafer has a thickness in the range of approximately 100 to 1000 microns.Thus, the high aspect ratio holes used to form the optical fibers can befabricated with a width that is in the range from approximately 0.5microns to approximately 10 microns.

[0021] Optical fiber 102 a is coupled to functional circuits 108 a and109 a. For example, optical transmitter 104 a is coupled to one end ofoptical fiber 102 a and optical receiver 106 a is coupled to a second,opposite end of optical fiber 102 a. Optical transmitter 104 a is alsocoupled to a node of functional circuit 108 a and optical receiver 106 ais coupled to a node of functional circuit 109 a. In one embodiment,optical transmitter 104 a comprises a gallium arsenide transmitter thatis bonded to the first surface of semiconductor wafer 100 a usingconventional wafer bonding techniques. In this embodiment, opticalreceiver 106 a comprises a silicon photodiode detector formed in thesecond surface of semiconductor wafer 100 a. In other embodiments, otherappropriate optical receivers and transmitters may be used to transmitsignals over optical fiber 102 a.

[0022] Optical fiber 102 a comprises cladding layer 112 a that separatescore 110 a from semiconductor wafer 100 a. In this structure,semiconductor wafer 100 a acts as the outer “sheath” for optical fiber102 a. Various materials can be used to form core 110 a and claddinglayer 112 a. Basically, core 110 a comprise a material with a higherindex of refraction than the material of cladding layer 112 a and thusprovides normal optical fiber waveguide characteristics. Specificexamples of materials for core 110 a and cladding layer 112 a areprovided below with respect to FIGS. 6 and 7.

[0023] Since the optical fiber is formed in a wafer of semiconductormaterial, absorption by and radiation in the semiconductor wafer canaffect the operation of the optical fiber. For example, if thewavelength of the light transmitted in optical fiber 102 a is greaterthan the absorption edge of the semiconductor wafer, e.g., 1.1 micronsfor silicon, then semiconductor wafer 100 a will not absorb the lighttransmitted in optical fiber 102 a. However, due to the large change inindex of refraction at the interface between cladding layer 112 a andsemiconductor wafer 100 a, some radiation loss occurs into semiconductorwafer 100 a. This case is depicted, for example, in FIG. 8.

[0024]FIG. 8 is a graph that illustrates the magnitude of the radiationin optical fiber 102 a along a diameter of optical fiber 102 a. In theregion of core 256, indicated at 801, optical waves are guided with nosubstantial loss along the length of optical fiber 102 a. Evanescentfields are present in the region of cladding layer 254 as indicated at802. These evanescent fields drop off to insignificant levels asindicated at 800 in the surrounding semiconductor wafer.

[0025] In the case of shorter wavelength light transmitted in opticalfiber 102 a, there will be some absorption as well as radiation into thesemiconductor substrate. For example, with a silicon wafer, light with awavelength of less than 1.1 microns produces some small losses due toabsorption and radiation into the silicon wafer.

[0026] In some cases, it is advantageous to limit the penetration of theoptical wave into semiconductor wafer 100 a. This avoids problemsrelated to possible photoregeneration of carriers in the surroundingsemiconductor wafer 100 a that might interfere with the normal operationof other integrated circuitry. To prevent optical waves from penetratingthe semiconductor wafer, the hole that houses the optical fiber can belined with a reflecting metal mirror prior to forming the claddinglayer. A technique for forming the metal layer is described in relatedU.S. Pat. No. 6,090,636, which application is incorporated by reference.

[0027] Optical fibers can be added to circuits using a conventionallayout for the circuit without adversely affecting the surface arearequirements of the circuit. Conventional circuits typically includepads formed on the top surface of the semiconductor wafer that are usedto connect to leads of the integrated circuit through bonding wires.Advantageously, the bonding wires of conventional circuits can bereplaced by optical fibers 102 a to allow signals to be passed betweenvarious integrated circuits of electronic system 105 a without the needto attach the individual integrated circuits to a printed circuit board.This allows a substantial space savings in the design of electricalsystems along with overcoming concerns related to signal loss ordissipation and interference with and by other integrated circuitrydevices in the electrical system.

[0028]FIGS. 1B and 1C show additional embodiments of electronic systemsusing optical fibers formed through integrated circuits to interconnectvarious integrated circuits. In the embodiment of FIG. 1B, integratedcircuits 108 b and 109 b are formed in working surfaces of semiconductorwafers 100 b and 101 b. Surfaces opposite the working surfaces ofsemiconductor wafers 100 b and 101 b are bonded together usingconventional wafer bonding techniques. Optical fiber 102 b transmitssignals between integrated circuits 108 b and 109 b. A portion ofoptical fiber 102 b is formed in each of the semiconductor wafers 100 band 101 b. In the embodiment of FIG. 1C, semiconductor wafers 100 c and101 c are stacked with the working surface of semiconductor wafer 101 cbeneath the surface of semiconductor wafer 100 c that is opposite theworking surface of semiconductor wafer 100 c. In this embodiment,optical fiber 102 c is formed within semiconductor wafer 100 c.

[0029]FIGS. 2, 3, 4, 5, 6, and 7 are views of semiconductor wafer 200 atvarious points of an illustrative embodiment of a method for formingoptical fibers through a semiconductor wafer according to the teachingsof the present invention. Functional circuit 202 is formed in an activeregion of semiconductor wafer 200. For purposes of clarity, the Figuresonly show the formation of two optical fibers through semiconductorwafer 200. However, it is understood that with a particular functionalcircuit any appropriate number of optical fibers can be formed.Essentially, the optical fibers are formed in the same space on thesurface of semiconductor wafer 200 that is conventionally used to formbonding pads for leads. In a conventional circuit, the leads of theintegrated circuit are connected to a printed circuit board which routessignals to other integrated circuits. The optical fibers advantageouslyremove the need for a printed circuit board to interconnect thefunctional circuits formed on individual semiconductor wafers.

[0030] As shown in FIG. 2, photo resist layer 204 is formed on surface206 of semiconductor substrate 200. Photo resist layer 204 is patternedto provide openings 208 at points on surface 206 where high aspect ratioholes are to be formed through semiconductor wafer 200.

[0031] As shown in FIG. 3, etch pits 210 are formed by standard alkalineetching through openings 208 in photo resist layer 204. Photo resistlayer 204 is then removed.

[0032]FIG. 4 is a schematic diagram that illustrates an embodiment of alayout of equipment used to carry out an anodic etch that is used toform high aspect ratio holes 250 of FIG. 5. Typically, holes 250 have anaspect ratio in the range of 100 to 200. Bottom surface 262 ofsemiconductor wafer 200 is coupled to voltage source 234 by positiveelectrode 230. Further, negative electrode 232 is coupled to voltagesource 234 and is placed in a bath of 6% aqueous solution ofhydrofluoric acid (HF) on surface 206 of semiconductor wafer 200.

[0033] In this example, illumination equipment 236 is also includedbecause semiconductor wafer 200 is n-type semiconductor material. Whenp-type semiconductor material is used, the illumination equipment is notrequired. Illumination equipment 236 assures that there is a sufficientconcentration of holes in semiconductor wafer 200 as required by theanodic etching process. Illumination equipment 236 includes lamp 238, IRfilter 240, and lens 242. Illumination equipment 236 focuses light onsurface 262 of semiconductor wafer 200.

[0034] In operation, the anodic etch etches high aspect ratio holesthrough semiconductor wafer 200 at the location of etch pits 210.Voltage source 234 is turned on and provides a voltage across positiveand negative electrodes 230 and 232. Etching current flows from surface206 to positive electrode 230. This current forms the high aspect ratioholes through semiconductor wafer 200. Further, illumination equipmentilluminates surface 262 of semiconductor wafer 200 so as to assure asufficient concentration of holes for the anodic etching process. Thesize and shape of the high aspect ratio holes through semiconductorwafer 200 depends on, for example, the anodization parameters such as HFconcentration, current density, and light illumination. An anodicetching process is described in V. Lehmann, The Physics of MacroporeFormation in Low Doped n-Type Silicon, J. Electrochem. Soc., Vol. 140,No. 10, pp. 2836-2843, October 1993, which is incorporated herein byreference.

[0035] As shown in FIG. 5, cladding layer 254 is formed on surface 252of high aspect ratio holes 250. Further, core 256 is formed within hole250 such that cladding layer 254 and core 256 comprise optical fiber258.

[0036] Core 256 has an index of refraction that is greater than theindex of refraction of cladding layer 254. Cladding layer 254 maycomprise, for example, a transparent dielectric film such as siliconoxide (SiO₂), aluminum oxide (Al₂O₃), a nitride, other oxide, or otherappropriate dielectric material. Cladding layer 254 is deposited with auniformity that allows light to be transmitted through optical fiber 258with normal optical fiber waveguide characteristics. When a nitride isused, cladding layer 254 can be deposited with the required uniformityusing the technique described in K. P. Muller, et al, Trench NodeTechnology for Gigabit DRAM Generations, 1996 IEDM Technical Digest, p.507-510 which is incorporated by reference. This technique allowsnitride films to be deposited at low temperatures and low depositionrates to insure uniform coverage of very deep trenches. A techniquereferred to as “atomic layer epitaxy” can also be used to depositcladding layer 254. Atomic layer epitaxy has been described for use withthe deposition of silicon oxide (SiO₂), See J. W. Klaus, et al, AtomicLayer Controlled Growth of SiO ₂ Films Using Binary Reaction SequenceChemistry, Appl. Phys. Lett. 70(9), 3 Mar. 1997, pp. 1092-1094, which isincorporated by reference. Further, atomic layer epitaxy has beendescribed for use with deposition of aluminum oxide (Al₂O₃). The atomiclayer epitaxy technique deposits material with a thickness of 1 to 2angstroms for a single binary reaction sequence. Thus, the techniqueadvantageously allows the high aspect ratio holes that house the opticalfibers to be lined with a uniform cladding layer.

[0037] In one embodiment, optical fiber 258 transmits light with awavelength that is greater than 1.1 microns. In this embodiment,cladding layer 254 comprises silicon oxide (SiO₂) with an index ofrefraction of approximately 1.5 or aluminum oxide (Al₂O₃) with an indexof refraction of approximately 1.7. Core 256 comprises lightly dopedpolysilicon. The lightly doped polysilicon has an index of refraction ofapproximately 3.4 and exhibits low optical absorption at wavelengths ofgreater than 1.1 microns. Optical fiber 258 of this embodiment is shownin cross section in FIG. 6.

[0038] In another embodiment, cladding layer 254 comprises silicon oxide(SiO₂) and core 256 comprises an oxide or nitride with a higher index ofrefraction, e.g., aluminum oxide (Al₂O₃). A cross section of opticalfiber 258 of this embodiment is shown in FIG. 7. Core 256 does notcompletely fill the center of optical fiber 258. Hole 262 extends alongthe length of core 256 through semiconductor wafer 200. However, as longas hole 262 has a diameter that is less than 0.59 times the wavelengthof the light transmitted over optical fiber 258, the light will still beguided by core 256 as shown in FIG. 9. This embodiment can transportlight with a wavelength that is less than 1.1 microns. This allows agallium arsenide emitter to be used at one end of optical fiber 258 totransmit signals down optical fiber 258 and a simple silicon photodiodedetector to be used as the receiver on the opposite end of optical fiber258.

[0039]FIG. 9 is a graph that illustrates the magnitude of the radiationin an optical fiber of the type shown in FIG. 7 along a diameter of theoptical fiber. In the region of hole 262, an evanescent field is presentas indicated at 900. In the region of core 256, radiation in the opticalfiber is guided along the length of the fiber without significant lossin intensity. Evanescent fields are present in the region of claddinglayer 254 as indicated at 904. These evanescent fields drop off toinsignificant levels as indicated at 906 in the surroundingsemiconductor wafer.

CONCLUSION

[0040] Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover any adaptations or variations of the presentinvention. For example, other materials such as oxides, nitrides, orhigh index glasses can be used to form the cladding layer and the coreof an optical fiber that extends through a semiconductor wafer. It isnoted that optical fibers 102 and 258 can transmit signals in eitherdirection through the semiconductor wafer by proper placement oftransmitters and receivers. Further, electronic systems can include morethan two semiconductor wafers with sufficient optical fibers formedthrough the semiconductor wafers to allow signals to be communicatedbetween the integrated circuits of the various semiconductor wafers.

[0041] Advantageously, using optical fibers according to the teachingsof the present invention allows electronic systems to be constructed inless physical space compared to conventional electronic systems byremoving the need for large printed circuit boards to interconnectvarious integrated circuits. This also provides the advantage ofreducing the cost of packaging integrated circuits for a particularelectronic system by allowing a number of circuits to be packagedtogether. Further, using the optical fibers assures the electricalintegrity of interconnections between integrated circuits by reducingthe physical length of electrical interconnections between devices. Thisreduces concerns with signal loss or dissipation and interference withand by other integrated circuitry devices.

What is claimed is:
 1. An electronic system, comprising: a semiconductorsubstrate having a first surface, a second surface opposite the firstsurface, and a hole extending through the semiconductor substrate andconnecting the first surface and the second surface; a first functionalcircuit on the first surface of the semiconductor substrate; an opticalfiber in the hole, the optical fiber having a cladding layer and a core,the optical fiber also having a first end and a second end; an opticaltransmitter located at the first end of the optical fiber; and anoptical receiver located at the second end of the optical fiber, whereinthe optical transmitter and the optical receiver are configured totransmit optical signals through the semiconductor substrate between thefirst functional circuit and a second functional circuit.
 2. Theelectronic system of claim 1, wherein the optical transmitter and theoptical receiver are configured to transmit the optical signals from thefirst functional circuit to the second functional circuit.
 3. Theelectronic system of claim 1, wherein the optical transmitter and theoptical receiver are configured to transmit the optical signals from thesecond functional circuit to the first functional circuit.
 4. Theelectronic system of claim 1, wherein the cladding layer surrounds thecore, and a first index of refraction of the core is greater than asecond index of refraction of the cladding layer.
 5. The electronicsystem of claim 1, wherein the core of the optical fiber includes a corehole, the core hole running along the center of the optical fiber. 6.The electronic system of claim 1, further comprising a reflecting mirrorlining the hole.
 7. The electronic system of claim 1, wherein thecladding layer includes oxide material.
 8. The electronic system ofclaim 1, wherein the cladding layer includes nitride material.
 9. Anelectronic system, comprising: a semiconductor substrate having a firstsurface, a second surface opposite the first surface, and a holeextending through the semiconductor substrate and connecting the firstsurface and the second surface; a first functional circuit on the firstsurface; a second functional circuit on the second surface; an opticalfiber in the hole, the optical fiber having a cladding layer and a core,the optical fiber also having a first end and a second end; an opticaltransmitter located at the first end of the optical fiber; and anoptical receiver located at the second end of the optical fiber, whereinthe optical transmitter and the optical receiver are configured totransmit optical signals through the semiconductor substrate between thefirst functional circuit and the second functional circuit.
 10. Theelectronic system of claim 9, wherein the cladding layer includes SiO₂.11. The electronic system of claim 9, wherein the cladding layerincludes Al₂O₃.
 12. The electronic system of claim 9, wherein theoptical fiber is configured to transmit light having a wavelength, andwherein the hole includes a diameter of 0.59 times the wavelength of thelight.
 13. The electronic system of claim 9, wherein the opticaltransmitter includes gallium arsenide.
 14. The electronic system ofclaim 9, wherein the optical receiver includes a silicon photodiodedetector.
 15. The electronic system of claim 9, further comprising areflecting mirror lining the hole.
 16. An electronic system, comprising:a first semiconductor substrate having a first surface, a second surfaceopposite the first surface, and a hole extending through thesemiconductor substrate and connecting the first surface and the secondsurface; a second semiconductor substrate bonded to the firstsemiconductor substrate, the second semiconductor substrate having afirst surface and a second surface opposite the first surface; a firstfunctional circuit on the first surface of the first semiconductorsubstrate; a second functional circuit on the first surface of thesecond semiconductor substrate; an optical fiber in the hole, theoptical fiber having a cladding layer and a core, the optical fiber alsohaving a first end and a second end; an optical transmitter located atthe first end of the optical fiber; and an optical receiver located atthe second end of the optical fiber, wherein the optical transmitter andthe optical receiver are configured to transmit optical signals throughthe first semiconductor substrate between the first functional circuitand the second functional circuit.
 17. The electronic system of claim16, wherein the cladding layer includes oxide material.
 18. Theelectronic system of claim 16, wherein the cladding layer includesnitride material.
 19. The electronic system of claim 16, wherein thecladding layer surrounds the core, and a first index of refraction ofthe core is greater than a second index of refraction of the claddinglayer.
 20. The electronic system of claim 16, wherein the core of theoptical fiber includes a core hole, the core hole running along thecenter of the optical fiber.
 21. The electronic system of claim 16,further comprising a reflecting mirror lining the hole.
 22. Theelectronic system of claim 16, wherein the optical fiber is configuredto transmit light with a wavelength greater than 1.1 microns.
 23. Anelectronic system, comprising: a first semiconductor substrate having afirst surface, a second surface opposite the first surface, and a holeextending through the semiconductor substrate and connecting the firstsurface and the second surface; a second semiconductor having a firstsurface and a second surface opposite the first surface, wherein thesecond surface of the first semiconductor substrate is bonded to thesecond surface of the second semiconductor substrate; a first functionalcircuit on the first surface of the first semiconductor substrate; asecond functional circuit on the first surface of the secondsemiconductor substrate; an optical fiber in the first hole and thesecond hole, the optical fiber having a cladding layer and a core, theoptical fiber also having a first end and a second end; an opticaltransmitter located at the first end of the optical fiber; and anoptical receiver located at the second end of the optical fiber, whereinthe optical transmitter and the optical receiver are configured totransmit optical signals through the first semiconductor substrate andthe second semiconductor substrate between the first functional circuitand the second functional circuit.
 24. The electronic system of claim23, wherein the cladding layer includes SiO₂.
 25. The electronic systemof claim 24, wherein the core includes doped polysilicon.
 26. Theelectronic system of claim 25, further comprising a reflecting mirrorlining the hole.
 27. The electronic system of claim 24, wherein the coreincludes Al₂O₃.
 28. The electronic system of claim 23, furthercomprising a reflecting mirror lining the hole.
 29. An electronicsystem, comprising: a first semiconductor substrate having a firstsurface, a second surface opposite the first surface, and a holeextending through the semiconductor substrate and connecting the firstsurface and the second surface; a second semiconductor substrate havinga first surface and a second surface opposite the first surface, whereinthe second surface of the first semiconductor substrate is bonded to thefirst surface of the second semiconductor substrate; a first functionalcircuit on the first surface of the first semiconductor substrate; asecond functional circuit on the first surface of the secondsemiconductor substrate; an optical fiber in the hole, the optical fiberhaving a cladding layer and a core, the optical fiber also having afirst end and a second end; an optical transmitter located at the firstend of the optical fiber; and an optical receiver located at the secondend of the optical fiber, wherein the optical transmitter and theoptical receiver are configured to transmit optical signals through thefirst semiconductor substrate between the first functional circuit andsecond functional circuit.
 30. The electronic system of claim 29,wherein the cladding layer includes Al₂O₃.
 31. The electronic system ofclaim 30, wherein the core includes doped polysilicon.
 32. Theelectronic system of claim 31, further comprising a reflecting mirrorlining the hole.
 33. The electronic system of claim 29, wherein thecladding layer includes SiO₂ and the core includes Al₂O₃.
 34. Anelectronic system, comprising: a semiconductor substrate having a firstsurface, a second surface opposite the first surface, and a holeextending through the semiconductor substrate and connecting the firstsurface and the second surface; a memory device on the first surface; aprocessor on the second surface; an optical fiber in the hole, theoptical fiber having a cladding layer and a core, the optical fiber alsohaving a first end and a second end; an optical transmitter located atthe first end of the optical fiber; and an optical receiver located atthe second end of the optical fiber, wherein the optical transmitter andthe optical receiver are configured to transmit optical signals throughthe semiconductor substrate between the memory device and the processor.35. The electronic system of claim 34, wherein the cladding layerincludes SiO₂.
 36. The electronic system of claim 34, wherein thecladding layer includes Al₂O₃.
 37. The electronic system of claim 34,wherein the optical fiber is configured to transmit light having awavelength, and wherein the hole includes a diameter of 0.59 times thewavelength of the light.
 38. The electronic system of claim 34, whereinthe optical transmitter includes gallium arsenide.
 39. The electronicsystem of claim 34, wherein the optical receiver includes a siliconphotodiode detector.
 40. The electronic system of claim 34, furthercomprising a reflecting mirror lining the hole.
 41. An electronicsystem, comprising: a first semiconductor substrate having a firstsurface, a second surface opposite the first surface, and a holeextending through the semiconductor substrate and connecting the firstsurface and the second surface; a second semiconductor substrate bondedto the first semiconductor substrate, the second semiconductor substratehaving a first surface and a second surface opposite the first surface;a memory device on the first surface of the first semiconductorsubstrate; a processor on the first surface of the second semiconductorsubstrate; an optical fiber in the hole, the optical fiber having acladding layer and a core, the optical fiber also having a first end anda second end; an optical transmitter located at the first end of theoptical fiber; and an optical receiver located at the second end of theoptical fiber, wherein the optical transmitter and the optical receiverare configured to transmit optical signals through the firstsemiconductor substrate between the memory device and the processor. 42.The electronic system of claim 41, wherein the cladding layer includesoxide material.
 43. The electronic system of claim 41, wherein thecladding layer includes nitride material.
 44. The electronic system ofclaim 41, wherein the cladding layer surrounds the core, and a firstindex of refraction of the core is greater than a second index ofrefraction of the cladding layer.
 45. The electronic system of claim 41,wherein the core of the optical fiber includes a core hole, the corehole running along the center of the optical fiber.
 46. The electronicsystem of claim 41, further comprising a reflecting mirror lining thehole.
 47. The electronic system of claim 41, wherein the optical fiberis configured to transmit light with a wavelength greater than 1.1microns.